We thought they cared about each other and it turns out, they actually do! A barn owlet squawks less when it knows its sibling is hungrier. Once the hungry sibling has been fed, an owlet will increase its own squawking. How sweet is that? (Okay, we know it is part of a survival strategy, but still, much more sibling bonding and cooperation than we ever would have thought to see in raptors.)

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Some photographers take reality... and impose the domination of their own thought and spirit. Others come before reality more tenderly and a photograph to them is an instrument of love and revelation. Ansel Adams

The barn owl has provided some of Springwatch’s most memorable moments. But hidden beneath its graceful, ghostly exterior is one of nature’s most finely tuned killing machines. Dominic Couzens reveals all.

A wavering, ghostly shape appears out of the gloaming, floating silently over a field. Your heart misses a beat and your senses seem to burst and freeze at the same time. It’s the barn owl, one of Britain’s most charismatic and sought-after birds. An encounter with this species is both thrilling and a little unsettling at the same time.

But why? To be honest, the pale plumage, small eyes and somewhat severe, heart-shaped face tend to cut the barn owl adrift from the friendly, ‘wise old owl’ persona of children’s literature – the one exuded, for example, by the tawny.

Instead, the barn owl appears more ghostly, more other-worldly and, especially when flying low along a beat on the edge of a field, it just seems to look more mechanical than other owls and birds. If you agree with this last impression, then you might be interested to know that it is closer to reality than you might have first thought.

Complex wiring

The barn owl isn’t a machine, of course, but within that head is an extraordinarily complex web of senses, a battery of detectors and wiring that would do credit to any modern electronic creation. In fact, it’s such a busy information highway that there probably isn’t enough room for wisdom.

The barn owl has to make its living in an exceptionally difficult way – catching fast-running animals that hide in dense foliage in the dark – and so it requires concomitantly extraordinary abilities.

Sharp ears

Its sight is excellent in low light, but its true headline ability is its hearing. Indeed, there is a case to be made for the barn owl having the most acute and strongly targeted hearing of any animal in the world.

Some years ago, American scientists performed a remarkable experiment with this species. They light-proofed a 14m by 4m room and covered the floor with dead leaves to a height of 5cm. Then they introduced a barn owl and a number of deer mice intothe controlled conditions.

They allowed the bird to acclimatise and then turned off all the lights, making it completely dark. Amazingly, they found that the owl could still hunt successfully without using its eyes; all it needed to make a kill was to hear the rustle of the mice in the leaves. Furthermore, when the owl, flying blind, struck, it almost never missed.

Silenced feathers

There are several astonishing aspects to this discovery, but let’s deal with the least obvious first.

If we accept that the barn owl more or less always hunts in flight, then we have to appreciate that, if it is to hear so subtle a sound as the rustling of a mouse, its own flight must be silent. This is quite a feat and achieved by a number of adaptations to the bird’s plumage.

Firstly, all of the wing feathers have a soft, downy surface, which eliminates the noise of them rubbing together. Secondly, the primary wing feathers (those that form the wing tip) have a fringe guarding their leading edge that is a bit like a comb and helps to order the flow of air smoothly over the wing.

Thirdly, the trailing edges of the wing feathers also have soft, hair-like fringes, which apparently damp down any turbulence created by the streams of air that meet behind the wing. These latter features are hard to understand without a knowledge of aerodynamics, but at least we can admire the fact that they do work.

Then, of course, we can marvel at the accuracy of the barn owl’s hearing – it found the small mice in a big room. It would be worth carrying out an experiment to see whether a human could catch a mouse by hand in complete darkness (do have a go and let me know how you get on).

How barn owls hear

The difference between this bird and a human is in the way it detects and locates sound. Here, once again, the barn owl has some remarkable adaptations.

In terms of actually picking up noise, studies have shown that its heart-shaped facial disc – such a clear and distinctive feature of the species – is made from stiff feathers that reflect any sound towards the ear openings on the sides of the head, thus amplifying the overall signal.

This is the principle of the parabola, where an umbrella-like reflecting surface, such as a satellite dish, concentrates widely separated waves into a point. The importance of the facial ruff is such that if the feathers are removed experimentally, the barn owl can no longer catch prey in the dark. With it, however, this bird can detect sounds that are too quiet for us even to pick up.

Selective hearing

Now, here’s a truly scary fact. Those in the know about the barn owl reckon that this bird’s auditory senses are so good that it can be selective while hunting.

This owl is so adept at distinguishing between frequencies that it is thought it can tell whether a rustle or squeak in the vegetation below is being made by a woodmouse or a bank vole. There is a distinct probability that it can also tell whether it is an adult or juvenile, or perhaps even a male or female – and who knows what else?

In our ignorance as observers, we might think that all the owl requires when it’s hunting is to find something – anything – to eat. However, a barn owl leaving its roost at dusk may have other ideas, equivalent to us thinking: “I fancy a Chinese tonight.”

Pinpoint precision

However, that’s not all. One of the barn owl’s most extraordinary adaptations is related to how it can pinpoint sounds: in other words, telling precisely where a noise is coming from.

Humans can do this quite well by assessing the minuscule time difference that the sound waves register when they reach each of our two ears. If the sound is to our left, for example, we will hear it in our left ear before our right ear, albeit only a tiny fraction of a second earlier – but still enough for our senses to appreciate the difference.

The barn owl can do this, too. However, its hearing has an extra dimension. The ear openings on either side of its head are not opposite each other; the one on the left is slightly higher than the one on the right. This means that a sound coming from directly below will be picked up by the right ear before the left ear, and thus the vertical difference will be accentuated.

Background disturbance

Now, this is all very well in the quiet of a blacked-out room, but the barn owl faces a very different set of conditions in the wild. Its world will normally be crowded by extraneous noises and interruptions, such as wind and the sounds of other animals and people.

Once again, we should sit back and be amazed that this bird can cope with such confusion – think how difficult it is for us to concentrate when there is a busy soundtrack in the background.

What big eyes you have!

But, of course, the barn owl also has eyes to complement its ears. They are almost certainly not as good as the eyes of many other owls that live in woodland, such as the tawny, but they are still well adapted for working in low light.

They are large (in comparison to many birds), tubular and packed with light-detecting rod cells, which make them particularly efficient at picking up movement and contrast, though admittedly at the expense of detail (the barn owl probably finds pure sight-hunting easier by day when it can use its colour-sensitive cone cells).

Another technical advantage, which is obscure to us but doubtless of great importance to the owl, is that its eyes have a powerful muscle that allows the cornea and lens to adjust rapidly, accommodating the changing focus as the hunter homes in rapidly on prey.

And, of course, their eyes are forward-facing. This arrangement naturally ensures that the visual field of each eye substantially overlaps that of the other eye, as it does in humans; it’s called binocular vision.

This enables the barn owl to judge distance, because a single point observed by two eyes at the same time is naturally detected from two slightly different angles since the eyes are set a small distance apart on the face. Once again, it is a differential in perception that enables the bird to be so accurate at homing in on potential prey.

Bird or machine?

There is something quite eerie about all this, though. Imagine, for example, that you are a mouse. If a barn owl is coming towards you and you rustle, it will hear you in three dimensions; and if you are foolish enough to move, it will also see you in three dimensions. That’s a pretty serious battery of instruments.

In fact, doesn’t it all sound a bit mechanical, perhaps?

HOW CAN I SEE BARN OWLS?

Distribution One of the best places to see barn owls is in Norfolk where they seem to be everywhere, night and day. However, the birds are widely distributed and likely to be somewhere near you, too.

Habitat Barn owls love rough, unmanaged fields and field margins. Look for them at the edge of woodland and along forest tracks, too. They also search for prey along ditches and reedbed margins.

Weather Avoid rainy evenings and excessively windy days. The best conditions are still and fair. However, in the middle of winter in heavy snow, barn owls are often forced to hunt during the day.

Some photographers take reality... and impose the domination of their own thought and spirit. Others come before reality more tenderly and a photograph to them is an instrument of love and revelation. Ansel Adams

Barn OwlsBill GraceyThis set is an attempt to document, in a small way, the owl nesting house we had installed on our property during the winter of 2011, and the owls that have been hatched there, and lived there while they were learning to fly and feed themselves. Within ten days of having the house installed, a nesting pair of Barn Owls moved in, and eventually two young owls were hatched there. We had this owl house installed because we wanted a natural way to control the rodents (particularly gophers) that are so prevalent in our area, and because we like birds, and were hoping we'd get a glimpse of these beautiful birds. This house was more successful than we'd hoped, and both we, and our neighbors, have noticed a large drop in the local rodent population, and when the young birds are learning to fly, we get to sit out after dusk and watch them with binoculars. Before the young owls can fly we've seen the parents bringing food to the young owls. We've received a lot of enjoyment from watching the owls.http://www.flickr.com/photos/9422878@N08...57630045851110/

Some photographers take reality... and impose the domination of their own thought and spirit. Others come before reality more tenderly and a photograph to them is an instrument of love and revelation. Ansel Adams

Some photographers take reality... and impose the domination of their own thought and spirit. Others come before reality more tenderly and a photograph to them is an instrument of love and revelation. Ansel Adams

Some photographers take reality... and impose the domination of their own thought and spirit. Others come before reality more tenderly and a photograph to them is an instrument of love and revelation. Ansel Adams